Social stressors, iron deficiency anemia, and lead exposure are all environmental risk factors for poor neurodevelopment in young children. All three factors are highly prevalent in poor communities, whether in Mexico or the U.S. There are scant human epidemiologic studies on chronic social stress and human neurodevelopment. In addition, previous studies of child development and neurotoxicants have typically analyzed covariate markers of social stress as independent predictors of neurodevelopment; and thus, only considered social factors as potential confounders in their data analysis. There are biological reasons to believe that stress potentiates the toxicity of iron deficiency anemia and lead poisoning. If so, then understanding this relationship may be the key to designing effective public health interventions designed to improve neurodevelopment and may explain the lack of effectiveness of prevention/treatment regimens for lead poisoning and iron deficiency. A prospective cohort study with a large sample size is needed to address the potential multiplicative effects of combined stress/iron deficiency anemia and combined stress/lead exposure in predicting infant development. This resubmission includes new data from a pilot study of stress-lead/stress-anemia interactions in 120 mother infant pairs conducted since the prior application, which demonstrates study feasibility and evidence for the hypothesized interactions. In this proposal we will measure maternal stress levels, infant iron deficiency anemia and lead exposure in a cohort of mother-infant pairs living in Mexico City and longitudinally measure maternal stress, iron stores, lead exposure, salivary cortisol and neurodevelopment beginning pre-natally and extending 3 years post-partum. This project will determine the independent effect of pre- and post-partum maternal stress in predicting infant development, and the multiplicative joint effects of maternal stress/iron deficiency and maternal stress/lead poisoning in predicting infant development.